I have had a lot of sucess with spot-tone, match the colour to the paper you are using.. a little secret I like is using a very good brush, Most people I see spotting use a nose-hair size tip, I use a windsor newton series 7 finest sable brush #2, it has a larger brush but in actual case you are only using the point of the brush to ****drop**** a slight tone into the area you are working on. As well this brush allows you to gather an larger amount of dye to continually drop in a defined pattern into the spot.
I find the trick is to camoflage the area and work with adjacent densitys to hide the spot.
In colour look closely at the grain of the print with a loupe, you will find it is a series of colours. Isolate those colours on your pallette and drop them randomly into the dust mark and slowly build up the density.
Put on some good music and enjoy yourself because no-one else will clean up these dust mites, so you should get good at it. I am suprised at how many technicans I meet , do not know how to spot well.
Also a very important point, I just turned 50 and my eyesight at close distances was getting shaky to say the least. Go to a local drugstore and get those simple reading glasses, it made a world of difference for me. Now I drop the dyes with pinpoint accuraccy rather than a random bombing pattern.